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Date: Tue, 15 Nov 2022 00:49:23 -0800 From: Deepak Gupta <debug@...osinc.com> To: debug@...osinc.com Cc: aou@...s.berkeley.edu, jan.kiszka@...mens.com, kbingham@...nel.org, linux-kernel@...r.kernel.org, palmer@...belt.com, paul.walmsley@...ive.com Subject: [PATCH v3] scripts/gdb: add lx_current support for riscv csr_sscratch CSR holds current task_struct address when hart is in user space. Trap handler on entry spills csr_sscratch into "tp" (x2) register and zeroes out csr_sscratch CSR. Trap handler on exit reloads "tp" with expected user mode value and place current task_struct address again in csr_scratch CSR. This patch assumes "tp" is pointing to task_struct. If value in csr_scratch is numerically greater than "tp" then it assumes csr_scratch is correct address of current task_struct. This logic holds when - hart is in user space, "tp" will be less than csr_scratch. - hart is in kernel space but not in trap handler, "tp" will be more than csr_scratch (csr_scratch being equal to 0). - hart is executing trap handler - "tp" is still pointing to user mode but csr_scratch contains ptr to task_struct. Thus numerically higher. - "tp" is pointing to task_struct but csr_scratch now contains either 0 or numerically smaller value (transiently holds user mode tp) Patch also adds new cached type "ulong" in scripts/gdb/linux/utils.py Signed-off-by: Deepak Gupta <debug@...osinc.com> --- scripts/gdb/linux/cpus.py | 15 +++++++++++++++ scripts/gdb/linux/utils.py | 5 +++++ 2 files changed, 20 insertions(+) diff --git a/scripts/gdb/linux/cpus.py b/scripts/gdb/linux/cpus.py index 15fc4626d236..ca5215a660c7 100644 --- a/scripts/gdb/linux/cpus.py +++ b/scripts/gdb/linux/cpus.py @@ -173,6 +173,21 @@ def get_current_task(cpu): else: raise gdb.GdbError("Sorry, obtaining the current task is not allowed " "while running in userspace(EL0)") + elif utils.is_target_arch("riscv"): + current_tp = gdb.parse_and_eval("$tp") + scratch_reg = gdb.parse_and_eval("$sscratch") + + # by default tp points to current task + current_task = current_tp.cast(task_ptr_type) + + # scratch register is set 0 in trap handler after entering kernel. + # When hart is in user mode, scratch register is pointing to task_struct. + # and tp is used by user mode. So when scratch register holds larger value + # (negative address as ulong is larger value) than tp, then use scratch register. + if (scratch_reg.cast(utils.get_ulong_type()) > current_tp.cast(utils.get_ulong_type())): + current_task = scratch_reg.cast(task_ptr_type) + + return current_task.dereference() else: raise gdb.GdbError("Sorry, obtaining the current task is not yet " "supported with this arch") diff --git a/scripts/gdb/linux/utils.py b/scripts/gdb/linux/utils.py index 1553f68716cc..ddaf3089170d 100644 --- a/scripts/gdb/linux/utils.py +++ b/scripts/gdb/linux/utils.py @@ -35,12 +35,17 @@ class CachedType: long_type = CachedType("long") +ulong_type = CachedType("ulong") atomic_long_type = CachedType("atomic_long_t") def get_long_type(): global long_type return long_type.get_type() +def get_ulong_type(): + global ulong_type + return ulong_type.get_type() + def offset_of(typeobj, field): element = gdb.Value(0).cast(typeobj) return int(str(element[field].address).split()[0], 16) -- 2.25.1
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